To provide a blood collecting set that can be sealed automatically.

The blood collecting set contains a needle constructing goods having a hub to which a needle cannula is attached to be fixed and the needle hub contains a fin that forms a ratch. A safety sealed is inserted to the hub and the needle cannula and movable from a base end position where the needle cannula is exposed to the end position where the needle cannula is sealed safely. The fin of the ratch is connected to the safety sealed as opening is possible when the sealed is in the base end position. A spring makes the sealed move in the end direction against the hub as the sealed surrounds the needle cannula corresponding to the movement of the ratch between the sealed and the hub.